Croft



. 3 Sheets-Sheet 2.

deL) I J."S. BANGROP T.- MACHINE FOR POINTING DRILLS.

Patented Mar; 9, 1886.

u. PETERS PM 3 sheets-sheet 3.

(Model) J ,S BANOROPT MACHINE FOR PQINTING YDRILLS. No. 337,549.

Patented Mar. 9

UNrren STATES ATENT @rrica.

JOHh SELLERS BANCROFT, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO W'ILLIAM SELLERS, OF SAME PLACE.

MACHINE FOR POINTING DRILLS.

ioPECIl-ICATION forming part of Letters Patent No. 337,5e9, dated March 9, 1886.

Application died May 1, 1884. Serial No. 129,933. (Modch) To all whom it may concern:

Be it known that I, JOHN SnLLnRs BAN- CROFT, of the city and county of Philadelphia, and Stateot' Peni'isylvania, have invented certain new and useful Improvements in Machines for Pointing Drills, of which the following is a specification.

In all drills there is necessarily a certain thickness of metal left between the two sides of the drill to hold them together-as, for ex;

ample, the web left between the two spiral grooves in a twist-drill-and hence the two cutting-edges do not meet, and the line which connects them, formed at the intersection of :5 the two surfaces to which the lips are ground,

is the soc-alled point of the drill. The thickness of the point is the length of this line and varies with thickness of the metal in the center of the drill and the amount of clearance given to the lips. This point offers great resistance to the progress of the drill through the work on account of the vary obtuse angle at which the surfaces forming the point m et,

thus making the action at this line ofjunction rather one of scraping than ofcut ting. and of course the resistance increases as the thickness of the point is increased with the size of the drill. With large drills the thickness of this web to give the'requircd strength to the lips is so great that it has long been recognized as necessary to reduce the point by grinding it away, so that the two flat sides of a flat drill,

or the two concave sides of a twist-drill.will

converge more rapidly toward the point. This 5 grinding, or pointing, as it is technically termed,has pi'iorto my invention been performed exclusively by hand, without the aid of machinery other than a revolving grinding wheel or stone. \Vhen so performed, however, it

0 requires great care for the most expert workman to thin the point so that it will be even approximately central between the two cutting-edges of the drill.

In the patent granted to J. Sellers Bancroft,

this applicant, and \Vm. H. Thorne for a machine for sharpening drills, No. 270,365, dated January 9, 1883, means are shown and described for grinding the lips of a drill so that the two cutting-edges shall be exactly the same angle with and equidistant from the o axis of the drill. and the apex of the convex point so produced will be exactly on this axis; but if the metal forming the web of the drill is not central one cutting-edge will be longer than the other; hence the two cutting-edges would not work exactly alike and the size of the hole would be uncertain. It has therefore been found necessary for accurate work to point the drills after they have been thus sharpened.

It is the first object of my invention, therefore, to point a drill so that the axis of rotation, from which the two cuttingedges are equidistant and about which they revolve at the same angle of inclination, shall be exactly in the center of the above-defined point of the drill, and the point itself shall be of the minimum practical thickness.

It is a further object of my invention to hold the drill to be pointed accurately in its true position without depending upon exceptional skill on the part of the operator; and to these ends the nature of my invention consists in mechanism for chucking and clamping the drill so that I am enabled to grind away each side of the point of the drill or reduce the point by forming on each side of the point a surface inclined to a planepassing equidistant from and between the two cutting-edges, these surfaces being also equidistant from the axis of the drill; and it further consists in mechanism for automatically conforming the width of the surfaces to the diameter ofthe drill to he pointed.

In the accompanying drawings, which form part of this specification, Figure 1, Sheet 1, represents an elevation of my invention with the jaws for holding the drill removed so as to show the grinding-wheel in contact with the drill. Fig. 2, sheet 2, is a plan showinga o drill in position in thejaws. Fig. 3 is an enlarged plan of the jaws for holding the drill. Fig. 4 is an elevation of part of Fig. 3, showing the means for guiding the jaws. Fig. 5, Sheet 3, is an elevation of Fig. 3, showing the 5 stops on the jaws for accurately determining the position ofthe drill to be pointed. Fig. 6 is a plan of the wheel holding and guiding mechanism shown in position for pointing the l as above defined, is presented to the grindingsmallest drill for which the machine is calculated. Fig. '7 is an end elevation of part of Fig. (5. Fig. .8 is a plan of the parts shown in Fig. 6 in position for pointing the largest drill the machine is calculated to grind. Fig. 9 is a projection of the grindiugavheel on a plane passing through the eenterot' the wheel and at right angles to its path when the wheel holding and guiding mechanism is in the position shown in Fig. 8. Figs. 10 and 11, Sheet 1. are side and end views, respectively, of a twist drill pointed by my improved machine. Figs.

12 and 13 are sideand end views,respectively, of a fiat drill pointed by the same means.

In all the figures similar letters refer to similar parts.

The operation is the same whether the drill operated upon is flat or twist.

The drawings show the machine about onehalfsize.

A, Figs. 1 and 2, represents the bed of the machine.

B, Fig. 2, Sheet 2, shows a drill in position for pointing. The back end of the drill is carried by the sliding back center, D, which slides freely on the rod C,seeuredin the stand A. The cenlerD is retained in alignment by a feathersliding in a groove in the rod 0, and is clamped by the nut S, so as to steady the end of the drill B, which is held firmly against the center D after itslongitudinal position has been fixed by the end stop, a, hereinafter described. When the drill is turned over to have the other side olthe point ground, it is held firmly against the center I) while reclamping the cutting end. The cutting end of the drill is clamped between the faces 0 and p on the jaws E and F, the drill being first rotated by hand until its lips rest against the stops Z and m on the jawsF and E, respectively, in which position it is retained by the hand of the operator during the process of grinding, (see FigsS and 5,) theloi'igitudinal position of the drill being determined, a; above mentioned, by the end stop, a, on the jaw E, so that the drillis accurately chucked or clamped in po' sition radially by the clampingtaces 0 and j), circuml'erentially by the stops Z and m, and longitudinally by the end stop, a. The corner formed by the meeting of the two faces 0 and a is so located near the-axis of the cylindrical part of the jaw E that it will always move in the same line relatively to the guiding-slot in the block G without being affected by the angle at which this block may be clamped.

To locate the reduced point of the drill between the two cuttingedges, so that these edgesshall be equidistant from itand of equal length, it is essential that the cutting-edges shall be held accurately, so that the outer ends ofthe cutting-edges shall be equidistant from the axis about which they revolve, and so that these ends and the axis of the drill shall he in the same fixed plane, and in the same position longitudinally when either side of the point,

wheel.

It will be observed that any method of grasping the body ot'a drill in a chuck or laying the drill in the groove for the purpose of pointing is undesirable, first, because these methods would be applicable. to twist drills only; and. second, because it is impossible by such methods of holding to be certain that the point will be central between the two cutting edges, since any crookedness in the drill or irregular spacing of the flutes will vary the position of the end of the drill as it is turned over in the ehuclc. It is consequently essential for the accurate location of the reduced point that the drill should be held by the outer ends of the two cutting-edges, and these outting-edges, or the edges of the flutes immediately adjoining these cuttingedges, should be heldagainststops-such asZandm-to fix their position relatively to the grindingwheelthat is to say, the drill should be held or chucked radially and circu|nfereulially with reference to its cutting-edges. If the drill is thus held or chucked and the grinding-wheel is brought to bear upon the point so as to re' duce it slightly, and the drill is then turned hall'-way round (being held against the back center, I), to prevent longitudinal motion, the end stop, a, being used only to determine the position of the drill when first chucked) and again grasped by the same surfaces, and the grinding-wheel again brought to bear upon the reversed point without any change in the adjustment of the wheel, it will result in the point being absolutely central between the two cutting-edges.

It will be evident that, instead of the back center, D, the end stop, a, may be used to determine the position of the drill in both chuckings; but this requires that the back center, D, shall be held against the drill by a spring or its equivalent to prevent side motion on the conical center.

The clamping jaws E and F are made cylindrical on their clamping ends, which are supported by the blocks G and H, as shown in Figs. 3, 4, and 5. the clan'iping-l'aces 0 and p and stops 1, m, and n being formed on the upper ends of these cylinders,while the lower ends slide in slots h and j in the guiding-blocks G and H. These slots or grooves confine the motion of the jaws in right lines laterally, while the enlarged portion otthe arms of the jaws fit in grooves a and b,which preveutvertieal motion of the jaws. These cylindrical ends of thejaws E and F, in connection with the pivot-screws cand d in the lever N, leave free the angular adjustment of the blocks G and H withoutin any manner interfering with the bearing and support of the jaws in the blocks. 'lhejaws E and F are moved in and out to grasp a small or large drill by means of the lever N, pivoted at T, Fig. 2. The short armsot this lever are ol'equal length, and the arms of the jaws E and F are attached thereto ICC by the pivot-screws c and d, respectively, so as to vibrate freely about these screws. When the lever N is vibrated about the center T, the jaws E and F are simultaneously and equally moved to or from the center line of the drill B.

It is essential that the points of the drills to be ground should always come in the same position relatively to the path of the grindingwheel, and therefore the jaws E and F must move in lines parallel with the cutting edges of the drill, and, as the angles which these edges make with each other may be varied ac cording to the nature of the work to be performed, the guide-blocks G and H are made adjustable about the center e, asshown in Fig. 3, and their inner edges are set to correspond with the proper graduations onthe base-plate to conform to the angle of the drill lips, the boltsfandf' (shownin dotted lines) being used to clamp the blocks in the desired position. These blocks should be adjusted so that the slots h and j, which guidethe cylindrical portion of thejaws,-shall be parallel to the cutting edges of the drill B. The center line of these slots h andj is radial to the center e, about which the blocks G and H rotate, and the centers of the cylindrical portion of the jaws will therefore move in radial lines, and hence all drills, of whatever diameter within the range of the machine whose cutting-edges are at the same angle as that to which the blocks G and H are set will have their-respecti\ e points brought to exactly thesame position relatively to the path of the grindingwhecl.

k The grinding-wheel I travels in a circular path that has for its radius the link M and for its center the pivot U. The axis of the pivot U being inclined, as shown in Fig. 1, the line of motion of the wheel I is at a considerable an gle with the axis of the drill, as indicated by the line y 3 Fig. 1. so that the greatest depth of the cut made by the wheel will be at the extreme end of the drill, this cut rapidly de creasing in depth as it extends back from the extreme end, and hence the supports to the cutting-edges of the drill are not weakened by thinning the center, as is usually the case in hand-grinding. The path of the cuttingline of the wheel is indicated by the line 3 y in Figs. 2 and 3,and it will be seen that it passes between the line of the axis of the drill and its cutting-edge. The wheel I is secured on one end of a mandrel, which turns freely in the bearing J, and is driven by the cord-pulley V, secured to the opposite end. The belt driving this pulley V passes under the fixed pulley \V, and also under the tightener-pulley X, carried by the weighted arm Y, which is piv- 4 oted at Z. The path of the belt is indicated by broken lines in Fig. l. The tightener-pulley accommodates the belt to the varying position of the pulley V. The vibrating frame L is supported so as to swing freely on the pivots U and 7c, fastened in a stand formed with or secured to the bed A, the axes ofthe pivots U and It being in the same axial line and inclined to a horizontal plane, as shown in Fig. 1, for thepurpose abovedescribed. Theframe K is pivoted on the vibrating frame Lby pivots g and T, which are parallel with the pivotsUaud k. The other end of the frame Kcarries the adjustable rod 8. to which is secured the bearingJ, as shown in Fig. 7, Sheet 3. The rod 5 is provided at its upper end with a screw-thread, which engages with the adjusting or feed nut t, whichregulates the height of the wheel I by sliding the rod 8 through its hearings in the frame K. The nut t is graduated on its circum fereuce, so that the grindingwheel may be set to the same distance from the axis of the drill for each side of the point, the same graduation being made to coincide with the mark or index z'on the index-link R. The pivot u is secured firmly in the bearing J, so that its axis, if prolongcd,would intersecttheaxisofthegrindingwheel at a right angle, and pass through the point in its circumference, where it touches or is tangent to the drill to be ground. This pivot u turns and slides freely in the radius-link M and index link R. From this combination it follows that the point of tangcncy of the wheel with the drill will always move in a fixed path, determined by the length of the radius-link M and the position of the fixed pivot U. The frame K and radius-link M are of equal length. The distance between therod sand pivot a is equal to the distance between the pivots U and r. and this method of carrying the grinding-wheel thus forms a parallel motion, and, as the rodsis parallel to the pivot u and in the plane of the grinding-wheel, it follows that the wheel I will remain parallel to a plane passing through the pivots U and r in all parts of its path. In Fig. 6 these parts are shown in position for pointing the smallest drill for which the machine is adapted, the broken line y 3/ showing the path of the pivot u and of the corresponding point of tangency ot'the wheel I with the drill. The line 2 2 shows the path of the rod 8. In this case itwill be observed that the cut made by the wheel I will be but little wider than the thickness of the wheel itself, as when the wheel is at the extreme end of the drill its center plane is tangent to the path described by the pivot u. and the cut made in thedrill will be wider than the wheel only by the amount of the versed sine of the are through which the wheel swings while in contact with the drill. A cam, P, on the inner end of vibrating frame L is pressed against a boss, 0, on the lever N by a spiral spring, to, which rotates the lever N in the direction to close the jaws E and F, and hence grips any drill held between the jaws with a force due to the strength of the spring w.

In Fig. 6, Sheet 3, the boss 0 is shown in contact with the cam P in the proper position for the smallest drills the machine is calculated to grind, the broken circle 0 showing the position of the boss 0 when the largest drill the machine is intended to grind is clasped between the jaws. In Fig. 8 the cam P is shown IIO as moved over to this position, thereby moving the vibrating frame L through an angle of about fifteen degress, the effect being to swing the axis of the grindingwheel I through the same angle about the pivot to in a plane parallel with the path in which its grindingsnrface operates without changing the position of the pivot a, which still describes the same are y y about the fixed center U, and consequently the point of tangency of the wheel with the drill also moves in the same path as before. The pivot 1' being shifted by the movement of the vibrating frame L, the rod 8 describes the path z 2 about this new position, so the center plane of the wheel is still parallel to the plane passing through the pivots U and r, and the profile of the wheel relatively to its path at the point of the drill is represented in Fig. 9, so the cut made in the point by the wheel will now be much Wider than before.

By properly proportioning the cam P and lever N it is possible to vary the angle of the axis of the wheel I in a plane parallel to the path in which its grinding-surface operates to any desired extent proportioned to the size of the drill to be pointed, and when this position is once determined in the construction of the machine. the operator has only to see that the blocks G and H are set to the angle to which the drill-lips are ground, after which the operation of elaspiug the drill between the jaws E and F by means of the clampinglever N automatically adjusts the grinding-wheel to the proper angle. The spi ral spring 'w,through the pressure of the cam P against the lever N, tends to hold the jaws E and F against the drill. The back center, D, is now moved up so as to hold the end of the drill, and the operator, placing his hand on the radius-link M, moves the wheel I back and forth over the point of the drill 13, the amount of cut at each stroke being adjusted by the feed or adjusting nut t. Then one side is properly pointed, the lever N is pushed back so as to open the jaws, the drill is turned over, the lips coming against the stops Z and m. as before, and the 5 wheel is passed over this side of the point of the drill until the graduation on the adjustingnut t is at the same mark as before, when the surfaces on each side of the point will be at exactly the same distance from the axis of the drill, and consequently the chisel edge or point will be central, and the drill thus pointed, assuming that its lips have been properly ground, will produce accurate work.

In the foregoing description the traverse of the grinding-wheel has been described as being in a circular path of comparatively short radius. The length of this radius is not essential, as it may be extended indefinitely, it being requisite only that the grinding-surface of the wheel should be guided in a fixed path, the width of the path being varied by adjusting the axis of the wheel in a plane parallel to the path in which its griuding-surl'ace operates.

Having now deseribed my invention. what I claim as new, and desire to secure by Letters Patent, is-

1. In a drill-pointing machine, agrindingwheel operating in a fixed path with its axis variable in a plane parallel to the path in which its grinding-surface operates, whereby the width of the path may be increased or diminished, substantially as and for the purpose set forth.

2. In a drill-pointing machine, the combination of a grinding-wheel,a snpporting-franle therefor vibrating about an axis perpendicular to the axis of the grimling-wheel, drill-clamping jaws, and a lever connected to said jaws and engaging said wheel carrying frame, whereby the movement of the lever to operate the clamping-jaws adjusts the wheel-carrying frame with relation to the jaws and varies the width of the path of travel of the grinding-wheel to correspond to the size of the drill held by the clamping-jaws.

3. In a drill pointing machine, clampingjaws for holding the dril,in combination with supports which guide the clamping-jaws in lines parallel to the cutting-edges of the drill, substantially as and forthe purpose set fort-h.

4. The adjustable guiding-blocks G and H, in combination with the clan'iping-jaws Eand F for holding the drill, whereby the movements of the clamping-jaws are made parallel to the cutting-edges of the drill, subslantially as and for the purpose set forth.

J. SELLER-S BANCROFI.

Wit nesses:

CHAS. M. M ILLER, J os. H. SOHRACKE. 

